1. Field of the Invention
This invention relates to a novel process for preparing a compound, especially to a process capable of preparing, at around a normal temperature, such a compound which is difficult to produce by a conventional process or which can be produced only at a high temperature.
2. Prior Art
In conventional processes for preparing an objective compound, for example, in an organic synthetic chemical field, raw materials are introduced into a reaction vessel in a simple manner, the processing conditions such as pressure, temperature, and the like are appropriately selected, and a stirring treatment is entirely performed to proceed the synthesis. Also, when the synthetic reaction is performed with the intention of synthesizing the compound under milder condition such as at a lower temperature under a lower pressure, a catalyst having fixed activities is introduced into the reaction system.
At this time, a catalyst having specific activities on the reaction system is selected and a solid catalyst is often used as the catalyst.
Generally, the catalytic activities of these catalysts are defined by the characteristics of the catalyst, for example, physical and chemical characterization factors including the adsorbing behavior to materials composed of the reaction system, surface area, pore structure, atomic arrangement of the surface, state of crystal lattice defect, and degree of acidity or basicity. This suggests that no solid catalyst having catalytic activities to every reaction system can be prepared. Specifically, a specific catalyst having specific catalytic activities corresponds to a specific reaction system.
For example, a transition metal such as Ni, Pd, Pt, or the like is used for hydrogenation of an unsaturated hydrocarbon; transition metal oxide such as MoO.sub.3, V.sub.2 O.sub.5 is used for selective oxidation of an organic compound; and SiO.sub.2, Al.sub.2 O.sub.3, zeolite, or the like is used for cracking of hydrocarbon or isomerization of a hydrocarbon as a solid catalyst.
In conventional methods for using a solid catalyst, the catalytic activities exhibiting only depending on the above physical and chemical characterization factors which the solid catalyst itself possesses is utilized. Hence there are limitations to the degree of the activities. Also, there is no guarantee that a material exhibiting high catalytic activities on a desired synthetic reaction is always available.
On the other hand, there is a case where an objective reaction does not rapidly proceed, for example, at normal temperature even if a solid catalyst is utilized in a reaction system. In this case, it is necessary to supply certain energy externally to the reaction system.
Generally, as the above energy, heat energy is conventionally used, specifically, to heat a reaction vessel externally and thereby to maintain a reaction system in a required high temperature condition. The above reaction system includes the known reaction in which stable oxides of carbon such as CO.sub.2, a carbonate ion (CO.sub.3.sup.2-), or the like are reduced to synthesize hydrocarbon or other useful organic compound. The reaction system of this type has attracted remarkable attention as a method for absorbing CO.sub.2 from an atmosphere to transform it to a useful compound by utilizing excessive energy or natural energy though it has lately been apprehended that the increase in the concentration of CO.sub.2 was a cause of the rise in the temperature of the earth.
The synthetic reaction in this reaction system is known as the reaction for producing CO according to the following formula (1) and producing a higher hydrocarbon according to the following formula (2), which are described in Catalyst Lecture Vol. 9, page 84, (edited by Catalyst Society; published by Kodan Co., Ltd.): EQU CO.sub.2 +H.sub.2 .fwdarw.CO+H.sub.2 O (1) EQU nCO+(2n+1)H.sub.2 .fwdarw.C.sub.n H.sub.2n+2 +nH.sub.2 O (2)
Here, a temperature close to 1000.degree. C. is required to progress the reaction of the formula (1) sufficiently. It is, therefore, necessary to heat a reaction vessel externally, resulting in large-scale installation.
Also, the reaction of the formula (2) is so-called "Fisher-Tropsch reaction". This reaction is progressed by method in which a catalyst is fed into a reaction vessel and CO and H.sub.2 are introduced into the reaction vessel.
The reaction of the formula (2) is an exothermic reaction so that it is fundamentally unnecessary to supply energy required for reaction. However, it is necessary for the reaction system to be controlled at 150.degree. C.--several hundreds degree .degree. C. under normal pressure--10 atms to accelerate the reaction velocity sufficiently even if a solid catalyst such as Co is fed.
However, even though the heat energy supplied externally to the reaction vessel is indispensable for activating the materials involved in the reaction, it is not always required for other materials. Even in this case, it is required to heat the entire of the reaction system uniformly in a conventional method for supplying heat energy.
In the conventional method for supplying heat energy, an excessively large amount of heat energy is supplied to the reaction system. There is the drawback of a large energy loss in relation to the supply of the heat energy to be required for the objective reaction system.
Also, the equipment for synthesis requires large-scaled installation and the system in which the heat energy is externally supplied indispensably causes high costs taking measures for heat resistance and anti-corrosion into consideration.
On the other hand, an electrolytic synthetic system is known as a peculiar synthetic system.
In this electrolytic synthetic system, a specific electrolyte is filled in a reaction vessel in which a pair of electrodes consisting of positive and negative poles are disposed. Voltage is induced between the electrodes so that an electrochemical reaction is formed on the surface of the electrodes and thereby to synthesize a target compound.
In this reaction system, the energy required for the reaction is supplied directly to the materials in the reaction vessel in the form of electric energy. Therefore, it is unnecessary to heat the reaction vessel externally to supply heat energy to the reaction system even if the reaction system is endothermic reaction system.
In this electrolytic synthetic system, the surface of the electrodes disposed in the electrolyte is the actual field in which the synthetic reaction proceeds. In this system, therefore, the electrodes act as a kind of solid catalyst.
Incidentally, it is thought that the reactions of the above formulae (1) and (2) can be processed by the electrolytic reaction system. In this case, because the energy to be supplied is electric energy, the reactions of the formulae (1) and (2) can be carried out at around normal temperature. In view of this, various electrodes as the solid catalyst have been investigated.
However, in almost all of cases, only the reaction of the formula (1) proceeds to terminate the objective reaction or the products to be prepared are limited to very simple organic compounds such as methane, formic acid, and the like (see Chemistry and Chemical Industry, Vol. 43, page 2016-2017, 1990).
Specifically, it is difficult to progress a C--C bonding reaction and a hydrogen abstracting reaction for forming a C.dbd.C bond from a C--C bond in the conventional electrolytic synthetic reaction system.
In addition, since the catalytic activities of the electrodes acting as the solid catalyst are also defined by its physical and chemical characterization factors, it is required for heat energy to be supplied externally to the reaction system if the catalytic activity in the reaction system is insufficient.